This may seem silly, but how do they know that the effects we are seeing from dark energy, (which we only assume must be there due to observed acceleration), are not from gravity pulling us out from the other side?
Say there's all of this fast moving energy like light, and it extends further out than slower moving galaxies in the sphere of the entire universe.
Would the gravity of all those particles be enough to produce the observations that we assume are due to a pushing effect?